In the field of vehicle security checking, one of the present trends is to check container trucks and other various types of trucks without parking, thereby greatly improving security checking efficiency. In this case, it is necessary for drivers to drive vehicles through a radiation exposure region. As a result, it can cause great damage to the health of the drivers due to the high energy level or radiation dose of general accelerators or radiation sources. Thus, it is very important how to accurately recognize cabs where the drivers locate (the truck head portion) so that radiation sources may be controlled to perform no radiation or low level radiation on the cabs.
Cab recognition methods currently used in the field of security checking comprise adopting various sensors such as photoelectric switches or light curtains to recognize the type of vehicle, i.e., to recognize the head portion of the vehicle. Determining vehicle type using photoelectric switches is a determination based on blocking relationship of light beams, which requires a transmitting device and a receiving device, and thus occupies a larger area for mounting at fixed stations and cannot be mounted on vehicles for mobility.
Current vehicle type recognition is generally achieved by recognizing a gap portion between the head portion and the subsequent cargo portion of a vehicle using infrared photoelectric switches, induction coils or light curtains. For container trucks, the gap portion refers to a gap up to 1 meter between the head portion and the cargo portion of the vehicle; for van trucks, it refers to a gap about merely tens of centimeters or several centimeters between the head portion and the cargo portion of the vehicle; for some “single frame trucks”, it refers to merely a recess portion between the head portion and the cargo portion of the vehicle. Due to different types of vehicles, there may be different connection structures, distances and relative heights between the head portion and the subsequent cargo portion of the vehicle, leading to different gap portions accordingly. Thus, only using the single photoelectric switches or light curtains, it is difficult to accurately determine whether the ON or OFF of a light path indicates the true gap between the head portion and the cargo portion of vehicle or some other intervals, even causing a case in which windows may be recognized as the gap portion between head portion and the cargo portion of the vehicle. This usually causes errors in the recognition of positions of the head portion and the cargo portion of the vehicle using photoelectric switches or even two-dimensional images, putting drivers in danger or making radiation scanning area on images incomplete or inaccurate. For example, because there are windows in the cab, if a photoelectric switch is provided at such a height that a light beam passes the head portion of the vehicle through the open windows of the cab so as to arrive at a receiver opposite to the photoelectric switch, a controller may determines by mistake that the head portion of the vehicle has passed and thus turns on a radiation source. However, at this time, the head portion of the vehicle has not yet passed through the radiation scanning area in fact and this misoperation may bring great danger to drivers.
Thus, there is a need to provide a method and a system for recognizing the type of vehicle rapidly and accurately, which may rapidly and accurately distinguish the head portion and the cargo portion of a vehicle, so that a radiation source may be controlled accurately to emit radiations at an appropriate dose when it is necessary to emit radiations.